I found out today (thanks for the head's up Frank Perez) that v1.13 patch has a serious SecuROM problem that gives the exact problems I have been encountering over the last few days. Check out this post.
This is an absolute outrage, as it has caused me to waste many hours trying to resolve an issue that I thought was elsewhere on my computer, as I could see no reason why a patch to a game should have caused this degree of an OS issue. Now that I think about it, I can see how all the problems I had started a day or so after I did the patch. And the subsequent video issues were due to my reinstalling over the top to try to resolve the right-click issues.
Consequently, there was no time for our usual gaming session tonight as I did not have my computer ready in time, and it probably won't be now until tomorrow at the earliest. My fear now, of course, is that I have installed patch v1.13 again, and now I am worried that it will fail again soon.
I am too tired and angry at SecuROM to say anything more at the moment. And so I sign off feeling really frustrated that a company can get away with what amounts to placing legal viruses on someone's computer. Someone must be made responsible.
UPDATE: For those who have not yet gone through many hours of Windows reinstalls and have found this post, you can have an easy fix by running this official repair: http://www.securom.com/support/repair.zip
UPDATE: It sounds like Obsidian have also released a HotFix patch that resolves the problem now, as another Update. (Talk about bad timing for me.)